I'm surprised to hear that gnome-core requires gnash. It's certainly not
the case on Lenny:
I it was introduced into squeeze yesterday (source package meta-gnome2
2.28+6 transitioned to squeeze on 2010-03-16). The reason seems to be
that swfdec was removed. The changelog[0] for meta-gnome2 says (among
other things):
* Drop swfdec-gnome.
* Make gnome depend on mozilla-plugin-gnash so that there’s at least
something for Flash websites.
[0]:
<http://packages.debian.org/changelogs/pool/main/m/meta-gnome2/current/changelog>
/ johan